1. Field of the Invention
The present invention relates to a laminated material comprising a paper layer and a liquid-crystal polyester resin composition layer. More specifically the present invention pertains to a laminated material having excellent heat resistance, flexibility, and gas barrier properties as well as a paper pack container formed from the laminated material.
2. Description of the Related Art
Paper pack container whose one or both surfaces are processed with polyolefin have various advantages, that is, light-weight, unbreakable, inexpensive, and sufficiently hygienic, and are widely used in food, beverage, and other industries. These paper pack containers, however, have insufficient gas barrier properties. Laminated materials of paper and a polyolefin film or an engineering plastic film have been developed to improve the gas barrier properties. Both the polyolefin film and the general-purpose engineering plastic film, however, still have insufficient gas barrier properties with respect to water vapor and oxygen. This often causes oxidation, deterioration, and rot of the contents in the paper pack container of these constituents. Another problem of the conventional paper pack container is insufficient heat resistance.
Several techniques have been proposed to solve such problems. For example, Japanese Patent KOKAI Publication No. 1-199880 discloses a paper pack container including a paper layer and a gas-barrier synthetic resin.
In another example, Japanese Patent KOKAI Publication No. 3-061040 discloses a laminate film including a poly-3-methyl-1-butene layer and a paper layer.
In still another example, Japanese Patent KOKAI Publication No. 3-153348 discloses a sheet laminate including a paper layer and a polymer layer of ethylene-vinyl alcohol copolymer.
In another example, Japanese Patent KOKAI Publication No. 5-154964 discloses a packaging material including a paper layer and a polymer layer of ethylene vinyl acetate copolymer.
None of these proposed Laminates including paper as the substrate, however, have sufficient gas barrier properties or heat resistance.
Another known example is a laminate of paper and a metal foil, such as an aluminum foil, which has excellent gas barrier properties but is not free from a variety of other problems; that is, readily causing pin holes, having poor flexibility, being not applicable to microwave ovens, and having difficulties in waste treatment due to the presence of the metal foil.